Conventionally, an uninterruptible power supply apparatus includes a converter configured to convert AC power supplied from a first AC power source to DC power, an inverter configured to convert the DC power to AC power, and a switching circuit configured to provide any one of the AC power generated by the inverter and the AC power supplied from a second AC power source to a load. When the AC power is being supplied from the first AC power source, the DC power generated by the first converter is stored in a battery and supplied to the inverter, and the AC power generated by the inverter is supplied to the load.
In a power failure state in which the supply of the AC power from the first AC power source is stopped, the DC power of the battery is supplied to the inverter and the AC power generated by the inverter is supplied to the load. When the inverter has a malfunction, the AC power supplied from the second AC power source is supplied to the load through the switching circuit. Therefore, even when the power failure occurs or even when the inverter has a malfunction, the operation of the load can be continued. Such uninterruptible power supply apparatus is disclosed in, for example, Japanese Patent Laying-Open No. 2010-124557 (PTD 1).